New backends

[joeldevlearning]

Expand the number of supported backends. Consider the following:

• [x] InMemory (no backing file)
• [ ] XML
• [ ] JSON
• [ ] CSV
• [ ] Entity Framework and SQLite
• [ ] REST API, with support for multiple clients and call back

[joeldevlearning]

The InMemory functionality is now implicit (still no option to change storage, but all storage goes through the Model and this is the defacto InMemory storage).

Next, are the following tasks:

• refactor IDataSource into IStorage and modify XmlStorage to implement it
• create config option to switch between in-memory and Xml

[joeldevlearning]

IStorage needs to represent a data access object and probably needs only a few methods:

• List findAll();
• List findById);
• List findByCanidateName();
• boolean insertVoteRecord(VoteRecord vr);

Some questions:

• Do you we need a transfer object? Or just List to pass around?
• Should poller handle dealing with IStorage, or should the model? (Probably poller)